Help with text output file...

Question

Here's my assignment:
I read multiple postfix equations from a text file. I want to create a result text file that will store the answers. How can I create a file in the same folder that stores the answers. Here is my code that I have written. I'm not sure what's wrong...
                   try{
                    // reads in the file name and lines
                    FileReader freader = new FileReader(fileName);
                    // Checks for the file name and makes the results consistent
                    if(fileName.toUpperCase().equals("POSTFIX1.TXT"))
                         outputFileName = "Result1.txt";
                    if(fileName.toUpperCase().equals("POSTFIX2.TXT"))
                         outputFileName = "Result2.txt";               
                    if(fileName.toUpperCase().equals("POSTFIX3.TXT"))
                         outputFileName = "Result3.txt";
                    FileWriter fwriter = new FileWriter(outputFileName);
                    //PrintWriter outputFile = new PrintWriter(fwriter);
                    BufferedReader inputFile = new BufferedReader(freader);
                    tempEquation = inputFile.readLine();
                    goodFile = true;
                    // loops through each file line (equation)
                    while(tempEquation != null)
                         System.out.println(Calculation(tempEquation));
                         fwriter.write(Calculation(tempEquation));
                         tempEquation = inputFile.readLine();
                    fwriter.close();
               // catches an invalid file name
               catch(IOException e)
                    JOptionPane.showMessageDialog(null, "ERROR");
               }

Answer 1

                      fileName = JOptionPane.showInputDialog("Enter the file name: ");
               try{
                    // reads in the file name and lines
                    FileReader freader = new FileReader(fileName);
                    // Checks for the file name and makes the results consistent
                    if(fileName.toUpperCase().equals("POSTFIX1.TXT"))
                         outputFileName = "Result1.txt";
                    if(fileName.toUpperCase().equals("POSTFIX2.TXT"))
                         outputFileName = "Result2.txt";               
                    if(fileName.toUpperCase().equals("POSTFIX3.TXT"))
                         outputFileName = "Result3.txt";
                    FileWriter fwriter = new FileWriter(outputFileName);
                    PrintWriter outputFile = new PrintWriter(fwriter);